Typically, a thermal environment inside an enclosure, such as a building, a vehicle or a cockpit of an aircraft, largely depends on parameters such as velocities, temperatures inside the enclosure, solar irradiation incident through a window glass and the like. For assessing thermal comfort inside an enclosure, it is necessary to evaluate the influence of the above-mentioned parameters on thermal sensation that an occupant actually feels inside the enclosure. Traditionally, thermal comfort assessment is performed through a predicted mean vote (PMV) approach as outlined in international organization for standardization (ISO) 7730 standards.
However, drawbacks with the PMV approach are that it is typically applicable under uniform and homogeneous conditions and it depends very much on empirical correlations which are based on various parameters (e.g., velocity, temperature, etc.). In summary, using the PMV approach in non-uniform thermal environmental conditions (that typically exist in aircrafts, vehicles and the like due to air velocity, differences between air and wall temperature and solar irradiation) may lead to incorrect prediction of the thermal comfort assessment.
Another conventional approach based on equivalent temperature (teq), as outlined in ISO 14505-2 standards, is an integrated measure of the effects of non-evaporative (dry) heat loss from a body of an occupant. The equivalent temperature (teq) refers to a temperature of an imaginary enclosure having a mean radiant temperature equal to an air temperature and still air in which an occupant has the same heat exchange rate by convection and radiation as in the actual conditions. As outlined in the ISO 14505-2 standards, teq is typically calculated either using an empirical formula or through experiments. However, using the empirical formula may not be sensitive to changes in the physical parameters around the occupant inside the enclosure and may not yield actual teq of the body of the occupant. Also, calculating teq experimentally requires using thermal manikins (e.g., dummy dolls for reproducing thermal characteristics of occupants) and this may often be limited by cost, time and accurate representations of the actual conditions inside the enclosure.